1. Field of the Invention
The invention relates to a method for displaying the operating range of an electric drive vehicle and to a corresponding display device which, in particular, is configured for carrying out the method by a computer program product according to the invention. In the method, the battery energy currently available in a vehicle is determined and from this a maximum operating range of the vehicle is derived. The battery is typically constructed in the form of an accumulator and delivers the electrical energy for the electric drive. For determining the maximum operating range, at least one battery service station is selected as a destination point in the method, i.e., a station at which charging or replacing a battery is possible, especially a home position in the sense of a private battery service station (at home, work or the like) or a power filling station in the sense of a public battery service station. Using a starting point as a basis, an accessibility threshold is then determined, in the case of the transgression of which the vehicle can no longer reach the destination point with the current battery energy and/or can no longer return to the starting point (as destination point). This accessibility threshold is also called the “point of no return”. The accessibility threshold is displayed as an operating range in a map illustration. The map illustration can consist, for example, of a digital map, a stylized map having some selected position information items, or, in the simplest case, of a map containing only one scale.
2. Related Art
In principle, it is a problem in the case of electric drive vehicles that the operating range, which is distinctly restricted compared with fuel-operated vehicles, entails distinct losses of flexibility for the driver in his route planning and reaching the desired destinations. To increase the acceptance of electric vehicles, it is necessary, therefore, to at least keep the driver well informed about the destinations which can still be reached by him.
For this purpose, displays are known in which a circle in a map illustration is used, the radius of which, starting from the center point of the circle as current location, specifies the limits of the area which can be reached in the case of a direct, i.e. radial route. Although the driver can then see whether he can still reach his destination on a direct route, the driver will not know exactly, however, when an intermediate destination is not located precisely on this radial route, whether he can still approach such an intermediate destination. Taking into consideration that a vehicle also may need to charge or exchange the battery in a battery service station at its final destination, the final destination will frequently not be the actual useful destination of the trip because of the possibility that charging or exchanging the battery might not always be available at the useful destination. The useful destination then actually represents the intermediate destination and the battery service station represents the actual final destination.
From U.S. Pat. No. 5,539,399 A, a display is known in which the operating range of an electric drive vehicle can be displayed on a road map in dependence on the current battery charge. This can be done in a simple manner by a circle around the current location or by marking the accessible sections of all routes which can be traveled from the current location. To increase the accuracy, topographic data of the individual roads or regions are taken into consideration in the calculation of the maximum operating range, which are also stored in a digital road map. The problem of intermediate destinations, described above, is not taken into consideration in this context so that it is left to the driver to evaluate whether, after an intermediate destination, he will still be able to reach the final destination at which the battery of the vehicle can be exchanged or charged.
US 2010/0094496 A1 discloses a display of the threshold of the maximum operating range and of a “point of no return” threshold, in the case of the transgression of which a return to a reference point is no longer possible with the current energy supply without charging or exchanging the battery. The reference point can be the home of the car user or a charging station. In the determination of the accessibility of a destination, it is initially determined whether a vehicle can reach the destination with the amount of charge currently present in the battery. If this is not possible, it is checked whether the vehicle can reach a battery service station, which is then added to an energy plan, it also being possible, if necessary, for a charging time at this station to also be taken into consideration. The display occurs in the context of route planning. A warning message is generated if the driver exceeds a “point of no return” threshold, i.e. can no longer reach a battery service station with the energy remaining in the battery. This is cumbersome in that the routes need to be planned elaborately and the next destinations must always be input or confirmed by the user. This is elaborate and complicated in the case of spontaneous route changes. Moreover, it is always necessary to wait for the updating of the route planning until the driver is able to decide whether he can actually drive the planned route.
EP 2 172 740 A1 discloses a method for displaying the operating range of an electric drive vehicle in dependence on a charging time of the battery and the location, the operating range being displayed in dependence on various charging periods starting with the current state of charge of the battery. At the same time, the road geometry, slope information, traffic information and/or information from a learning system can also be used. Although this makes it easier for the user, before starting the journey, to estimate the amount of energy needed for the next trip as charging time of the system relevant for him, the user must also ensure in this system that he can also still continue driving to a charging or exchanging station after reaching the desired destination.
From JP-A-2006-112932, a similar method is known in which a navigation device allows the user of an electrically operated vehicle to input a desired destination in order then to determine the arrival time, wherein, apart from the traveling time, the required amount of energy and possibly the time needed for charging the battery is also taken into consideration if the energy available in the battery is not sufficient for reaching the destination.
JP-A-2003-294463 describes an input or display and selection of charging stations in the vicinity of a desired destination for the purpose of calculating whether it is possible to continue driving as far as a charging station after reaching a destination. However, this does always require a destination to be input, which restricts the flexibility in utilization. Because there must always be a system-supported route planning, this hinders spontaneous route changes of the driver.